5 - Chapter3-VerticalCurves

5 - Chapter3-VerticalCurves - Geometric Highway Design...

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Geometric Highway Design: Vertical Curves TTE 4004 Lecture 5 9/9/11
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Attendance Quiz Which type of resistance usually has the greatest impact on a vehicle traveling on a highway? What are the two components of practical stopping distance?
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Geometric Design Elements Number of lanes Lane width Median type Median width Length of acceleration and deceleration lanes Need for truck climbing lanes Curve radii for vehicle turning Vertical and horizontal alignment
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Chapter 3 Outline Vertical Curve Design Vertical curve fundamentals Stopping sight distance Crest vertical curves Sag vertical curves Passing sight distance – crest vertical curves Underpass sight distance – sag vertical curves Horizontal Curve Design Vehicle cornering Horizontal curve fundamentals Stopping sight distance – horizontal curves Combination of horizontal and vertical curves
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5 Vertical Curve Profile Views Fig. 3.3
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6 Notation Curve point naming PVC: Point of Vertical Curvature PVI: Point of Vertical Intersection (of initial and final tangents) PVT: Point of Vertical Tangency Curve positioning and length usually referenced in stations Stations represent 1000 m or 100 ft e.g., 1258.5 ft 12 + 58.5 (i.e., 12 stations & 58.5 ft)
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7 Notation (cont.) G 1 is initial roadway grade Also referred to as initial tangent grade G 2 is final roadway (tangent) grade A is the absolute value of the difference in grades (generally expressed in percent) A = |G 1 – G 2 | L is the length of the vertical curve measured in a horizontal plane (not along curve center line, like horizontal curves)
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8 Curve Equation Parabolic curves are generally used for design Parabolic function y = ax 2 + bx + c y = roadway elevation x = distance from PVC c = elevation of PVC Also usually design for equal-length tangents i.e., half of curve length is before PVI and half after Eq. 3.1
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9 First Derivative of Equation First derivative gives slope At PVC, x = 0, so , by definition G 1 is initial slope (in ft/ft or m/m) as previously defined b ax dx dy + = 2 1 G dx dy b = =
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This note was uploaded on 12/07/2011 for the course TTE 4004 taught by Professor Staff during the Fall '08 term at University of Florida.

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5 - Chapter3-VerticalCurves - Geometric Highway Design...

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